1. From Web, click Page Designer 
  2. Click Next
  3. In the Colors & Styles 
  4. Click Advanced colors and styles
  5. Click edit style sheet
  6. Insert the following before the end of basic styles 
.MS_LoginButtonOuterContainer {
background:#FFA500 !important;
.MS_LoginButtonInnerContainer {
background:#FFA500 !important;
  1. Click Apply, click Save and Submit the changes

    Note: Replace #FFA500 with the color of your choice. In this example, it is changing the backgroud color to Orange. We also do not support CSS customizations as this is just a suggestive way to do this function.